A toolbox of tactics used to control invasive weeds in Waterton Lakes Park, but it still may not be enough

Waterton Lakes National Park has been on the front lines of some of the worst invasive weed problems in southern Alberta for a number of years.

“Waterton is a highly diverse site,” acknowledges park ecologist Robert Sissons. “We have roughly 1,200 plant species and about 10 per cent of those are ones that have been introduced over time. And a large portion of those would be what we would consider invasive. We do an environmental assessment of all our control programs, and once we get through that, and our control strategy has been given a pass through environmental assessment, we can use herbicides in a controlled fashion. We do not just rampage through the land and spray willy-nilly. Herbicides are one tool, and we have multiple other tools depending on the species and the time of the year.”

While many invasives currently keep the park’s natural eco-system under constant threat, requiring a concerted and co-ordinated control strategy, in recent years knapweed has become enemy number one for Sissons and his crew. The weed is challenging to control because it is so widespread and generates a huge number of seeds each year. The park uses a combination of spot application herbicides, bio-control insects and even hand pulling once the knapweed begins to flower in low density locations to try to contain and combat its spread.

“We do use hand pulling a lot,” he confirms. “For example, once knapweed starts to hit the flowering stage herbicides become less effective; so we then switch to hand pulling. We have crews drop their backpack sprayers and pick up some gloves and they go out and pull.

“We use pulling to target those areas where we might not be able to use herbicides, whether it’s a wildlife sensitive area or near water bodies,” he says.

Part of that hand-pulling strategy enlists the public’s help through the park’s annual Knapweed Rodeo, which took place this year on Aug. 17. The Knapweed Rodeo brings out about 30 volunteers on average, says Waterton public outreach officer Dianne Pachal.

“That’s a lot of knapweed which gets pulled,” she says. “It makes a big difference. Even one person volunteering, and pulling out one bag of weeds, that’s more than a square metre. That’s stopping over a quarter million seeds from spreading.”

Pachal says the annual event usually has a good representation from local farms and municipal districts alongside other friends of the park. These “good neighbours” come for various reasons, she says, but many from the ag community come out to learn more about knapweed so they can apply that knowledge to their own lands.

“They come because they want to be able to identify weeds, because they know it is important it not spread,” Pachal says. “They want to know what knapweed is, where it came from, how it got here, and what it is like to deal with it, as we as a park are doing. It’s a straight forward plant to identify once it is explained to you. Once you know it, you are not going to mix it up with something else. It is also straight-forward to pull. It’s got a taproot like a carrot; so it is amongst the easier weeds to pull.”

Sissons says knapweed is one of those weeds in the park which is beyond chemical control in certain regions. In that case, the park chooses to deploy bio-control insects for long term impact and follow a policy of containment rather than outright eradication.

“There are certain areas where there is a high density of knapweed, and those are treated as containment zones,” he confirms. “We just work around the periphery of those areas and try to stop the spread.” Replanting native seeds after eradicating or pulling invasives is also another important pillar in the park’s strategy, Sissons says.

“If you just pull weeds and walk away, the weeds will probably come back,” he explains. “We pull weeds, but we also have a program of restoration where we have collected our native seeds from plants in the park. We either seed those directly through a broadcast or hydro-seeder or we get lots of plugs growing out. We can plant several thousand plugs in an area. We try to get native plant communities re-establishing in those areas, and that helps to prevent the weeds from coming back.”

A few years ago, Sissons felt confident the park might finally be getting some kind of minimal handle on the knapweed problem; that is until the Kenow wildfire forced them to reset all their efforts as the knapweed flourished in the newly fire-cleared areas while local native species lagged behind. But knapweed is far from the only invasive weed which has flourished in the fire’s aftermath, Sissons says. His teams were also forced to step up control of ox-eye daisy, downey brome and other invasives.

But, Sissons admits, there was one invasive weed his control teams were completely helpless against last year.

“Lambs quarters (also known as pigweed) is a very low-key introduced plant that has been around the country for centuries,” he says. “It has a real longevity of seed in the soil; so after the fire opened up all that bare ground that one came back. That was a dominant plant on the landscape for last year, and it was beyond our ability to control. This year we did not notice as much of the lambs quarters. Once the native plants grew up, it wasn’t able to compete with those and it is now back to its normal distribution. In that case, we were able to kind of step back and watch and not try to control it. And we let nature take the lead in controlling that one.”

The battle against invasive weeds in Waterton Park is an unending one, says Sissons. Over the years, park staff have learned to pick their battles.

“There are some of these species which we have already accepted as part of the community— like dandelions. We don’t think of dandelions as an invasive species, but it is prevalent from grasslands to south alpine. It’s everywhere, but it is not dominant in any one spot. So bio-diversity and functioning of that eco-system can still work with dandelions in it. But it is those species like knapweed that we have to persevere on, and hope for new technologies and ways of controlling them sometime in the future— and in the near future, hopefully.”

Since there is no final victory possible against these invasives, Sissons says the park has had to change its definition of success.

“You have to repeat year after year, and over time you can make a difference,” he states. “Any time you can stop new seed production, you are winning the battle— slowly.”

Photo courtesy Parks CanadaWaterton Lakes National Park held its 26th annual Knapweed Rodeo on Aug 17. The Knapweed Rodeo is just one way the park engages with the public to raise awareness of invasive weeds. The park’s control methods include various levels of herbicide use, hand-pulling, reclamation and introduced biological control insects. Pictured: Volunteers help out at Knapweed Rodeo in 2018.